code: def attach_oauth(app: fastapi.FastAPI):
      try:
          from starlette.middleware.sessions import SessionMiddleware
      except ImportError as e:
          raise ImportError(
              "Cannot initialize OAuth to due a missing library. Please run `pip install gradio[oauth]` or add "
              "`gradio[oauth]` to your requirements.txt file in order to install the required dependencies."
          ) from e
  
      # Add `/login/huggingface`, `/login/callback` and `/logout` routes to enable OAuth in the Gradio app.
      # If the app is running in a Space, OAuth is enabled normally. Otherwise, we mock the "real" routes to make the
      # user log in with a fake user profile - without any calls to hf.co.
      if get_space() is not None:
          _add_oauth_routes(app)
      else:
          _add_mocked_oauth_routes(app)
  
      # Session Middleware requires a secret key to sign the cookies. Let's use a hash
      # of the OAuth secret key to make it unique to the Space + updated in case OAuth
      # config gets updated.
      session_secret = (OAUTH_CLIENT_SECRET or "") + "-v2"
      # ^ if we change the session cookie format in the future, we can bump the version of the session secret to make
      #   sure cookies are invalidated. Otherwise some users with an old cookie format might get a HTTP 500 error.
      app.add_middleware(
          SessionMiddleware,
          secret_key=hashlib.sha256(
              session_secret.encode()
          ).hexdigest(),
          same_site="none",
          https_only=True,
      )
  
file_path: gradio/gradio/oauth.py
imports: from __future__ import annotations
  import hashlib
  import os
  import typing
  import warnings
  from dataclasses import dataclass, field
  import fastapi
  from fastapi.responses import RedirectResponse
  from huggingface_hub import HfFolder, whoami
  from .utils import get_space
label_desc: Use image node_id 1 for calling a global function with example usage: attach_oauth(app) without return types